A concentration gradient takes place when ions or particles labeled as solutes begins to move from a higher concentration of particles in a solution to lower the concentration particles. A membrane separates both regions from each other. The membrane separating them can be either a permeable membrane, a semi-permeable membrane, or a non-permeable membrane. Almost all types of particles and ions can easily pass through the porous layer. The semi-permeable membrane only grants access to specific particles. Finally, the non-permeable membrane does not permit any atoms or particles to penetrate through it.
In biochemistry, concentration refers to the amount of solute in the solution. Whereas, gradient generally means the continuous increase or decrease of a variable respective to the distance.
There are two phenomena of transport in biology. Passive transport does not require any additional energy as the transportation of particles from higher intensities to lower intensities takes place along the concentration gradient. However, to carry out active transport, chemical energy is necessitated for moving particles against the concentration gradient from lower densities to higher densities.
Diffusion and concentration gradient
Simple diffusion is an example of passive transport. Where particles, atoms, or ions move from an area of higher concentration to lower concentration area by the assistance of a concentration gradient. When equilibrium reaches between the two regions, the movement slows down to the natural motion of particles. This process regularly runs between the intercellular fluid and external side of a human cell, exchanging both useful and waste products at the same time.
Osmosis and concentration gradient
Osmosis is very similar to diffusion as both involve the movement of particles along a concentration gradient. The actual difference is, which particle is moving. In osmosis, the solvent moves through the membrane while in diffusion, the solute moves through the membrane. An osmotic gradient is a pressure that forces solvent particles to move from a higher concentration to lower concentration. Since a water molecule is a polar molecule, it requires a transport protein to travel through the membrane.
No chemical energy is required to carry out this process as the movement is downhill.
Active transport and concentration gradient
In active-transport, molecules travel against the concentration gradient. The movement of particles from a higher concentration area to a lower concentration region demands chemical energy. Primary active-transport like adenosine triphosphate requires chemical energy. A secondary active-transport utilizes both electrical and chemical gradient. An electrochemical gradient is the gradient of an ion that defuses in the cell passing through a cell membrane. The diffusion of ions affects the electric potential of the cell membrane. If a charge gradient has occurred, the charged particles then follow a downhill movement.
Examples of the concentration gradient
Sodium symport pump
This pump uses a sodium/potassium gradient to move glucose and sodium. Glucose is relatively hard to drive compared to tiny sodium atoms, which often move against the concentration gradient. To resolve this issue, some cells couple the movement of glucose with the movement potassium taking assistance from a particular protein that will only allow the sodium atom to travel if it carries a glucose molecule with it.
Proton gradient also identified as the H+ gradient forms due to the difference in proton concentration between the internal and external sides of a membrane. Transportation of protons across the membrane by a protein named proton pump creates a proton gradient. The proton pump transports the protons to the inter-membrane space form the mitochondria resulting in an increased number of protons outside. Thus building up a proton gradient across the biological membrane.
Gases also involve in concentration gradient similarly to particles dissolved in different liquids. Humans and other living organisms obtain oxygen from their lungs/gills as oxygen also obeys the law of the concentration gradient. Lungs contain alveoli where the air is trapped when we breathe in. As soon as we inhale the air, oxygen diffuses inside our blood along the concentration gradient. There are capillaries across each alveolus, carrying deoxygenated blood, which speeds up the diffusion process.
Everyday examples of the concentration gradient
Whenever you use a room spray, you only spray it on one side of the room. However, after a while, the scent spreads in the entire room through diffusion along the concentration gradient. The difference in concentration of fragrance in the whole room creates a concentration gradient, which moves particles from a higher intensity to lower intensity, eventually establishing equilibrium in the entire room.
An unequal concentration of particles between two areas creates a concentration gradient moving the particles from the higher density region to the lower density area. The concentration gradient plays a vital role in establishing and maintaining the equilibrium in living organisms. Apart from living species concentration gradient also helps in managing the rules and regulations of nature. Without the presence of a concentration gradient, various basic life necessities, ranging from oxygen to the transportation of energy throughout the body, are impossible to achieve.